As a conventional cutting insert, Japanese Unexamined Patent Publication No. 2010-64224 and U.S. Pat. No. 7,494,393 disclose configurations of interposing a breaker groove between a cutting edge and a constraining surface.
However, with these cutting inserts in which the constraining surface and the breaker groove are formed in the same surface, chips generated by the cutting edge are apt to collide with the constraining surface, thus making it difficult to ensure stable chip discharge performance. Additionally, the constraining surface is worn and thus makes it difficult to ensure constraining stability.